More than 235,000 people have fled from their homes in Syria's rebel-held Idlib province, the UN says. The exodus happened between 12 and 25 December as fighting intensified.
Idlib in north-western Syria is the last major region held by rebels opposed to President Bashar al-Assad.
The Russian-backed Syrian government has been bombarding Idlib since late November.
An increase in air strikes and ground fighting since mid-December has accelerated civilian displacement from the area, UN humanitarian agency Ocha.
Tens of thousands of families - including some already displaced numerous times during the civil war - have been heading north in trucks and private cars.
The government offensive had left the city of Maarat al-Numan and the nearby region in southern Idlib "almost empty", Ocha said.
Most of the displaced civilians are moving to cities and refugee camps in northern areas of Idlib and neighbouring Aleppo province.
"Many who fled are in urgent need of humanitarian support, particularly shelter, food, health, non-food and winterisation assistance," the UN said. Thousands more families were "frightened to move, fearing the risk of air strikes and shelling along the routes", the UN said.